This is exactly what happened to me. I always scored between 167 and 172, went even as far as 178, but then I got 163 on the real test. I took it again and felt worse than after the first, so I had to cancel it. I took it this Feb for the last time, and I am expecting a higher score than the first two. For me, I think the first section made the difference. It's important that you do the first one without panicking. Another thing is that my expectation became much lower before the exam, thus the lower level of stress. But you should also know that my case is definitely exceptional. A great majority of the people I asked told me they got what they expected or even better. I guess I'm a pressure-prone person.